docs(*): add bare-metal guide

Adds some light documentation around bare metal provisioning.

closes #730
Merge pull request #979 from deis/baremetal_docs

docs(*): add bare-metal guide
Merge pull request #969 from deis/multiple_routers

feat(router): support for multiple routers
docs(*): update docs for local3.deisapp.com, local5.deisapp.com

We've created the convenience records for local3.deisapp.com and
local5.deisapp.com, so local clusters no longer have to manage
DNS whatsoever.

closes #747